Encoders for converting rotary or linear motion into digital signals representative thereof are readily available and well known in the art, and various different types of electronic circuits are available for utilizing the digital information generated by such encoders. In many applications, an encoder system is used to provide position information that is directly displayed to an operator by means of a digital display. In particular, the use of encoders for providing digital readout of positional information for machine tools is becoming more widespread.
Frequently, blueprints give dimensions for one point in a small area with respect to the work piece while dimensioning other points in the area relative to each other. It would be convenient for the machine operator and would eliminate mistakes caused by errors in doing mental arithmetic if the operator could have two different positional displays for each dimension, one display corresponding with the "absolute" position of the machine and the other display corresponding with the "relative" position of the machine.